Designing an Exoskeleton: Calculating Minimum Required Torque for Hip Joint"

[JAm1]

Hi I'm designing an exoskeleton that would be fitted to a persons leg. I've been doing some calculations to solve for the minimum required torque to carry a persons leg at the hip joint. The equation I'm using is..

Mhip = Mweight + Mexo + (Ileg + Iexo)*alpha

where:
Mhip = torque required at hip joint
Mweight = resisting torque produced by the weight of the leg
Mexo = resisting torque produced by the weight of the exoskeleton
Ileg* = moment of inertia of the leg
Iexo = moment of inertia of the exoskeleton
alpha = angular acceleration at hip joint

I've been doing some rough calculations based on some anthropometric data and I'm getting values around 40-50Nm(I used 30 degrees as the maximum angle for the leg) for Mhip.


My problem is this. Am I doing the mechanics correctly? is 40-50Nm a reasonable torque value? How/Where can i look for DC motors + gears that would accommodate this torque? Can i use relatively small motors then just gear it up to get my req torque?

Thanks to anyone who can help. I'm kinda new to this designing thing. But I'm really willing to learn.

 

[Unrest]

Mhip = Mweight + Mexo + (Ileg + Iexo)*alpha

I've been doing some rough calculations based on some anthropometric data and I'm getting values around 40-50Nm(I used 30 degrees as the maximum angle for the leg) for Mhip.

I guess you only want to move the leg, not actually assist walking. So that equation is reasonable. To visualise 40Nm, imagine lifting a 4kg object hanging off your shin, using your straight outstretched leg. (40N * 1m)

Can i use relatively small motors then just gear it up to get my req torque?

Yes, but it'll reduce the speed. power output of motor = torque * angular velocity

 

[JAm1]

Hi unrest, yes that is what i need it it to do, just lift the leg. Basically the application of this is for rehabilitation purposes. It just needs to move the leg to simulate walking. the effect of the weight if the person will be minimal because the person will be harnessed. I just needed to double check my equation.

By any chance can anybody refer me where i can get good dc motors? I know there's google, but hey at least i could start somewhere :)